1. Field of the Invention
The present invention relates to a technique for evaluating the quality of a moving image and, more particularly, to a technique for evaluating the smoothness of the motion of a video formed from a plurality of frame images.
2. Description of the Related Art
Conventionally, various methods to evaluate the smoothness of the motion of a moving image have been made open to the public. The smoothness of a motion degrades due to, for example, motion discontinuity (judder or jerkiness) or a blur. One factor that degrades the smoothness of a motion is frame rate conversion of the video source. Japanese Patent Laid-Open No. 2008-072665 proposes a technique of quantitatively evaluating the degradation in the smoothness of a motion caused by the frame rate conversion. More specifically, according to Japanese Patent Laid-Open No. 2008-072665, the sum of powers of spatial frequencies in an image is calculated for each frame in accordance with the visual spatial bandwidth corresponding to the moving speed of an object, thereby calculating the evaluation value.
The display characteristic of a device also largely affects the smoothness of a motion. Japanese Patent Laid-Open No. 2005-333564 proposes a technique of quantitatively evaluating the degradation in the smoothness of a motion caused by the display characteristic of a device. In Japanese Patent Laid-Open No. 2005-333564, a camera captures a chart moving on a screen while following up it. The time response characteristic of the display is obtained from the blur amount of the acquired still image, thereby calculating the evaluation value.
In the method described in Japanese Patent Laid-Open No. 2008-072665, the sum of powers of spatial frequencies in an image is calculated for each frame. Hence, in the method described in Japanese Patent Laid-Open No. 2008-072665, if the motion vector of the object largely changes between frames, the evaluation accuracy may lower. According to the method described in Japanese Patent Laid-Open No. 2005-333564, since the motion of the chart is compiled to one still image, the time-rate change of the motion of the chart is not reflected on the evaluation value. To evaluate the quality of a moving image, it is necessary to obtain an accurate evaluation value that more highly correlates with the subjectivity.